In accordance with the elucidation of the in vivo activity of thiol protease such as papain, cathepsin B, cathepsin H, cathepsin L, calpain or the like, it has been found that their extraordinary hypersthenia causes various diseases. Further, there is increasing the report which shows thiol protease inhibitors are effective on such disease in animal models.
It is considered that thiol protease such as calpain, cathepsin B or the like take part in the initial process such as disappearance of Z line through the decomposition of muscular fiber protein in the collapse of skeletal muscle as seen in muscular disease such as muscular Dystrophy, amyotrophy or the like [Taisha (Metabolism), 25, 183 (1988)]. Furthermore, E-64-d, namely a thiol protease inhibitor, has been reported to have life-prolonging effect in experimental muscular dystrophy hamster [Journal of Pharmacobio dynamics, 10, 678 (1987)]. Accordingly, such thiol protease inhibitors are expected to be useful as therapeutic agents for the treatment of muscular dystrophy, amyotrophy or the like.
The main cause of the post-ischemic cellular disorder occurs during ischemic diseases such as cardiac infarction, stroke and the like is active oxygen produced by xanthine oxidase. It has been reported that, during the ischemia, the increase in Ca.sup.2+ concentration results in the activation of calpain which restrictively degrade xanthine dehydrogenase, a precursor of xanthine oxidase, to give xanthine oxidase [New England Journal of Medicine, 312, p.159, (1985)]. It has also been reported that the activation of calpain may directly cause the necrosis of myocardial cells or neurocytes [Saishin Igaku, 43, p.783, (1988)]. There have been reported that NCO-700, a calpain inhibitor, is effective on cardiac infarction when tested on animal models [Arzneimittel Forschung/Drug Research, 36, p.190, p.671, (1986)], and that E-64-C inhibits the degradation of microtubule-associated protein after the brain ischemia [Brain Research, 526, p.177, (1990)]. These reports indicate that a calpain inhibitor can be useful for the treatment of ischemic diseases such as cardiac infarction, stroke and the like.
The cause of senile plaque which is found specifically in the brain of patients suffering from Alzheimer's disease is known to be the precipitated amyloid, a protein produced by the decomposition of an amyloid precursor protein (APP). Although APP does not give amyloid as a normal metabolite, it may be converted into amyloid under an abnormal metabolism where protease is extremely activated, and precipitated as senile plaque [Scientific American, (11), p.40, (1991)]. Therefore, protease inhibitor is expected to be useful for the treatment of Alzheimer's disease.
The activation of calpain has been observed in a brain trauma model of rabbit [Neurochemical Research, 16, p.483, (1991)]. It has also been observed, the administration of leupetin, a calpain inhibitor, can protect axon in brain trauma models of rat [Journal of Neurosurgery, 65, p.92, (1986)]. Thus, calpain inhibitors are considered to be useful for improving the conscious disturbance or motor disturbance caused by brain trauma.
It has also been reported that myelin-associated protein exists in dendrite of neurocytes is decomposed by calpain [Journal of Neurochemistry, 47, p.1007, (1986)], indicating that calpain inhibitors may be effective on diseases caused by the demyelination of neurocytes such as multiple sclerosis, peripheral nervous neuropathy and the like.
The main cause of the turbidity during cataract is hydrolytic products of a water-soluble protein crystallin by protease in lens. It has been observed the increase in calcium concentration in lens of cataractous animal models and some of human cataract [Investigative Ophthalmology & Visual Science, 28, p.1702, (1987); Experimental Eye Research, 34, p.413, (1982)]. The dominant protease contained in lens is calpain [Lens and Eye Toxicity Research, 6, p.725, (1989)]. These facts indicate that the abnormal sthenia of calpain can be one of the causes of cataract. There is a report that E-64, an inhibitor of calpain, is effective on cataract in animal models [Investigative Ophthalmology & Visual Science, 32, p.533, (1991)], indicating that calpain inhibitors can be useful in the treatment of cataract.
Neutrophils, which is deeply associated to inflammation, show the degranulation or production of superoxides in response to the stimulations by a chemotaxic factor or phorbol ester through a mechanism appeared to be mediated by protein kinase C (PKC). Calpain participates in the activation of PKC in the manner where it promotes the degranulation and inhibits the production of superoxides [Journal of Biological Chemistry, 263, p.1915, (1988)]. In another report, the concentration of cathepsin B in macrophage in rat is 30 to 40 times that of leukocytes and neutrophils, and the concentration of the enzyme in inflammatory macrophage is 6 times that of normal macrophages [Journal of Biochemistry, 98, p.87, (1985)]. These facts indicate that thiol protease inhibitors are useful as anti-inflammatory drugs.
The type I allergy reaction is mediated by immunoglobulin E (IgE) produced in the subject immunized with an antigen. Estatin A, a thiol protease inhibitor, has been reported to specifically inhibit the production of IgE without affecting on the production of IgG [The Journal of Antibiotics, 42, p.1362, (1989)]. Accordingly, thiol protease inhibitors are considered to be useful as antiallergic drugs.
In case of necrosis of hepatic cells, it is believed that impairment of the cell membrane leads to an increase in the permeability of Ca.sup.2+, an increase in intracellular Ca.sup.2+ concentration, an activation of calpain, and, as the result, the decomposition of its substrate such as skeletal protein takes place, which results in the death of cells. Accordingly, a calpain inhibitor can be used as a therapeutic agent for fulminant hepatitis.
Cathepsins such as cathepsin B and cathepsin L are involved in decomposition of bone collagen in osteoclast. It has been reported that administration of an inhibitor of cathepsins, E-64 or estatin A, to a rat which has an enhanced bone destruction by administration of parathyroid hormone leads to a decrease of calcium concentration and hydroxyproline concentration in blood [Biochemical and Biophysical Research Communication, 125, p.441, (1984): Japanese Patent Publication (kokai) No. 218610/1990]. Accordingly, it is believed that an inhibitor of cathepsins can be a therapeutic agent for osteoporosis, hypercalcemia and the like.
There exist, as a substrate for calpain, sex hormone receptors such as estrogen receptor and androgen receptor, and it is known that calpain activates these receptors. Accordingly, it is considered that an abnormal sthenia of calpain causes a disease which is suspected to be caused by an abnormal activation of the sex hormone receptors, for example, breast carcinoma, prostatic carcinoma or prostatomegaly. It is believed that an inhibitor for calpain can be a therapeutic agent for the above disease.
Receptors for epidermal growth factor (EGF) are also considered to be activated in association with the canceration of cells. It is known that calpain activates the EGF receptors as its substrate. Furthermore, it has been reported that calpain is activated in cells which have been infected with adult T cell human leukocyte virus (ATLV/HTLV-1) [Seikagaku, 57, p.1202, (1985)]. On the other hand, it is said that cathepsin B is greatly involved in a process of cancer metastasis because it accelerates decomposition of collagen which is a important step for the cancer metastasis or directly decomposes collagen, and because it has a profound correlation with plasma membrane of neoplastic cells [Tumor Progression and Markers, p.47, (1982); Journal of Biological Chemistry, 256, p.8536, (1984)]. These facts suggest that a thiol protease inhibitor has an ability to suppress the growth of cancer cells and prevent the metastasis of cancer.
Activation of platelet causes the aggregation thereof which is a cause of thrombus. It has been reported that an inhibitor of calpain, E-64-d, suppressed aggregation of platelet caused by thrombin [Thrombosis Research, 57, p.847, (1990)]. Accordingly, the inhibitor of calpain can be used as an inhibitor against aggregation of platelet.
As described above, an abnormal sthenia of thiol protease causes various diseases and a validity of several thiol protease inhibitors in animal models has been reported. However, most of known inhibitors, for example, epoxy succinate derivatives such as E-64 [Agricultural and Biological Chemistry, 42, p.529, (1978)], E-64-d [Journal of Biochemistry, 93, p.1305, (1983)], NCO-700 [Japanese Patent Publication (kokai) No. 126879/1983], and estatins A and B [The Journal of Antibiotics, 42, p.1362, (1989)], or .alpha.-substituted ketone of a peptide such as chloromethyl ketone [Journal of Biochemistry, 99, p.173, (1986)] and acyloxymethyl ketone [Biochemistry, 30, p.4678, (1991)] are irreversible inhibitors. It is generally said that the irreversible inhibitors are highly toxic because they are liable to react with non-specifically to components consisting living body, other than target enzymes. Therefore, there have been few compounds applicable to clinical use so far. Although peptidyl aldehydes such as leupeptin [The Journal of Antibiotics, 22, p.183, (1969)] or carpeptine [Journal of Enzyme Inhibition, 3, p.195, (1990)] are known as reversible inhibitors, they also have problems in chemical and in vivo stabilities, cell membrane permeabilities and the like.